linux-kernel - Re: [tip:efi/core] x86/mm/pat: Use _PAGE_GLOBAL bit for EFI page table mappings

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Message-ID: <CALCETrVDy2hB_eww8rB0FSWNJMiU0ZZOmWNxpcXsfmupiO8YLw@mail.gmail.com>
Date:	Wed, 24 Feb 2016 08:36:33 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Matt Fleming <matt@...eblueprint.co.uk>,
	Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>,
	"Ravi V. Shankar" <ravi.v.shankar@...el.com>,
	Toshi Kani <toshi.kani@...com>,
	Brian Gerst <brgerst@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Luis Rodriguez <mcgrof@...e.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>, ricardo.neri@...el.com,
	Hugh Dickins <hughd@...gle.com>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>
Subject: Re: [tip:efi/core] x86/mm/pat: Use _PAGE_GLOBAL bit for EFI page
 table mappings

On Wed, Feb 24, 2016 at 8:20 AM, Borislav Petkov <bp@...en8.de> wrote:
> On Wed, Feb 24, 2016 at 02:10:46PM +0000, Matt Fleming wrote:
>> > Normally, the only pages with are _PAGE_GLOBAL are those that are in
>> > the normal kernel mappings (swapper_pg_dir and normal mm_struct pgds).
>> > By allowing _PAGE_GLOBAL to be set in EFI mappings, you're breaking
>> > that convention, which forces you to use extra-expensive
>> > __flush_tlb_all calls in efi_call_virt.
>
> Hold on, do you mean the __flush_tlb_all() in the CONFIG_EFI_MIXED code?
>
> That's mixed mode. I think you mean the FLUSH_TLB_ALL in efi_call.
> That's EFI on 64-bit but that is mandated by the spec, AFAIR.

I mean the one in efi_call_virt.  Why would the spec mandate a TLB
flush at all?  EFI runtime services have no business touching the
paging structures directly.  Heck, the 32-bit ones don't even know the
*format* of the paging structures.

>
> So the EFI runtime crap should not change once it is mapped. And those
> should be global. It is only natural.

Why is it natural?

Long-term, I'd rather see EFI runtime services use an actual mm_struct
and use_mm.

--Andy